Question

I am trying to use the node-facebook-sdk to make FB graph API calls using Node.JS

I want to get feed data from all of a users friends.
FB graph API only allows 50 friends per batch request, so I am making a series of batch FB.api() calls.

I am trying to store the FB.api() calls in an array, then using jQuery when() to call the deferred functions.

problems:

1) the function I pass to the .done() function is executed prematurely.
2) the console.log(feed) is executed after .done(), which to my knowledge shouldn’t happen.

$ = require('jQuery');


//maximum batch size request is 50. use 2-D array to store in buckets of 50 friends each.
                var numFriends = friends.data.length;
                var batch = [];
                var deferred = [];//array to hold all the requests
                var feed_dump = [];//where we collect all the feed data

            //initialize a bucket for each set of 50 friends
            for (var i = 0, ii = numFriends / 50; i < ii; i++) {batch.push([]);}

            //put corresponding requests in in buckets.
            for (var i = 0; i < numFriends; i++) {
                batch[Math.floor(i/50)].push({ method: 'get', relative_url: friends.data[i].id + '/feed?since=' + '-1 month'});//not sure if the date format will work user.last_updated
            }

            //make the multiquery request for each bucket
            for (var i in batch) {
                var bucket = batch[i];
                //nested FB api call

                deferred.push(FB.api('', 'post', {'batch' : bucket}, function(res){//res = array 50 friend feeds
                        if (!res || res.error) {
                            console.log(!res ? 'error occurred' : res.error); return;
                        }
                        for (var j in res) {
                            var feed = JSON.parse(res[j].body);
                            console.log(feed);
                            feed_dump.push(feed);//feed for each friend appeneded to dump
                        }
                }));
            }

            console.log('this should show up before graph api requests are made.');

            //jQuery when() function.
            $.when.apply(null, deferred).done(function() {
                console.log('hopefully feed_dump has been updated...');
                PySocket.emit('update_user_graph',JSON.stringify(feed_dump));
            });

How can I defer the batch FB.api() requests properly? Also, if someone can think of a better way to do this, please let me know; I am not that experienced with async javascript.

I guess a simpler form of my question is : how can I wait for multiple callback functions to finish?

Thanks a bunch.

Answer 1

EDIT : Encapsulated callback count decrement : http://jsfiddle.net/3L9zc/32/

function BatchAPICalls(){
    var calls = [];
    var self = this;

    self.push = function(){
        var args = [];

        for(var i = 1; i < arguments.length - 1; i++)
            args.push(arguments[i]);

        calls.push({
            fn: arguments[0],
            callback: arguments[arguments.length - 1],
            args: args
        });        
    };

    self.start = function(callback){
        var callbacksLeft = calls.length;

        function batchCallback(){
            callbacksLeft--;
            if(callbacksLeft == 0)
                callback();
        }

        for(var i = 0; i < calls.length; i++){

            var call = calls[i];

            var batchItemCallback = function(){
                call.callback.apply(this, arguments);
                batchCallback();
            };

            call.fn.apply(this, call.args.concat([batchItemCallback]));            
        }
    };
}



var numFriends = friends.data.length;
var batch = [];
var feed_dump = [];

for (var i = 0, ii = numFriends / 50; i < ii; i++) {
    batch.push([]);
}

for (var i = 0; i < numFriends; i++) {
    batch[Math.floor(i/50)].push({ 
        method: 'get', 
        relative_url: friends.data[i].id + '/feed?since=' + '-1 month'
    });
}

function done() {
    console.log('hopefully feed_dump has been updated...');
    PySocket.emit('update_user_graph',JSON.stringify(feed_dump));
}    

var batchCalls = new BatchAPICalls();

for (var i in batch) {
    var bucket = batch[i];

    batchCalls.push(FB.api, 'call #' + i, 'post', {'batch' : bucket}, function(res){

        if (!res || res.error) {
            console.log(!res ? 'error occurred' : res.error); return;
        }
        for (var j in res) {
            var feed = JSON.parse(res[j].body);
            console.log(feed);
            feed_dump.push(feed);//feed for each friend appeneded to dump
        }
    });
}

console.log('this should show up before graph api requests are made.');

batchCalls.start(done);